(1) Field of the Invention
The present invention relates to antennas and more particularly to radiators for low profile, towed antennas.
(2) Description of the Prior Art
Present submarine communications with battlegroups or shore sites utilize surface antennas for a variety of requirements including SATCOM, LOS, etc. The use of surface antennas typically interferes with the covert operation of the submarine. For example, data exchange or the receipt of commands is accomplished by using antennas within a mast, which must be extended whenever transmission or reception is required. For communications in coastal or littoral areas, raising a mast renders the submarine vulnerable to visual or radar detection. To mitigate such detection, buoyant cable antennas (BCA) are often used. However, current BCAs cannot be used effectively for transmission, due to their extremely low radiation efficiency.
Furthermore, antennas towed on the ocean surface are subjected to dynamic forces that act to cause the antenna to pitch, yaw and sometimes roll under varying sea states. These antenna movements can easily result in transmission and reception interruption, especially so with the use of directional antennas. As a result, the towing submarine must operate in a station keeping status or must constantly adjust course headings in order to obtain optimal antenna performance.
In Rivera et al. (U.S. Pat. No. 6,127,983), there is disclosed a wideband antenna capable of transmission and reception while the antenna is towed horizontally in the ocean behind the submarine or vessel. Specifically, the antenna of the cited reference is formed as a metal cylinder having a longitudinal slot with the longitudinal slot open at one end and closed at the other end. The cylindrical shape in a towing container provides a strong righting moment to the antenna with the result of efficient broadband coverage under varying sea states.
Also, by setting the terminations of the antenna, that is, the open end, the closed end, and the feedpoint (along with the antenna diameter and thickness, and slot length and width) an antenna having a good impedance match over a wide frequency band is produced.
As disclosed, the above antenna is clearly suitable for wideband transmission when being towed in the ocean; however, an alternative antenna is desirable to produce an increased effectiveness during operation and an increased range of use when compared to the above antenna as well as for other known buoyant antennas.